Not applicable.
Not applicable.
Not applicable.
1. Field of the Invention
The present invention relates to a process for recovering protein suitable for an animal feed from animal manure. This process is operated to recover methane from biogas produced to supply the energy necessary for the successful economic operation of the process, which produces a protein-rich feed for livestock.
2. Description of Prior Art
The subject of how to treat manure to render it less noxious to the environment and to find suitable uses for it has long been investigated. As the population of various countries of the world have grown, so has the need for animals to supply protein to feed and nourish the growing populations. Thus, commercial operations have increased where poultry, hog, and cattle feeders and growers must enlarge their operations, but at the same time they face pressure for the removal of the animal waste produced by these animals. This manure, regardless of its animal source, can produce offensive odors and disposal problem by the shear amount that must be disposed of.
Also, as the populations increase they encroach further into agricultural areas. human residences are closer to feed lots or poultry houses. The waste-disposal problem then becomes greater since the volume of waste that cattle, hog, and poultry growers must dispose of becomes greater and the intervals between disposal get smaller. No longer can the waste merely be dumped on the land as fertilizer. To do so spreads not only the odor, but pathogens which may end up contaminating water tables supplying drinking water to the population. Drinking water contaminated by the field disposal of untreated, or even treated, animal waste can cause a myriad of diseases from its bacteria and unchecked viruses, which can produce streptococcus and staphylococcus infections, hepatitis, tetanus, tuberculosis, diphtheria and the like. Further, the pollution of streams caused by animal manure disposal can endanger the health of farm animals which graze the fields and drink from ponds or creeks which have been contaminated by water run-off from the spread of untreated animal waste.
This is not to say that the problem has not been long recognized with consequent attempts to reach a solution. For instance, U.S. Pat. No. 3,939,280 describes a method for processing poultry manure by adding an acid, particularly phosphoric acid, formaldehyde and urea to obtain a pathogen-free product suitable as an animal foodstuff for ruminant animals. An integrated system for hog production is described in U.S. Pat. No. 4,060,054 wherein the excrement is collected in a central place within the facility and treated by enzyme action and cooking, with stirring, to pasteurize the feed mixture, which is then cooled and fed back to the hog-feeding troughs as a part of the feed mixture. The is accomplished using heated waterfed from a boiler through a jacket about the cooker. A system for recovering single-cell proteins is described in U.S. Pat. No. 4,338,337, which employs a screening system for collecting the particulate waste to remove fines into the wash water used for collection of the animal waste. This process which is described in the context more of a hog barn or cattle feeding operation, employs an aerobic digestion of the fines and conversion into the single-cell proteins. The biomass such formed is recycled and used to flush the gutters of the facility to collect the nutrients into the feed material. U.S. Pat. No. 5,472,472 describes a process for biological transformation of phosphorus and nitrogen-containing animal waste into an ecologically-manageable material by making a precipitation step in a solids ecoreactor and passing the slurry into a bioreactor zone, where soluble phosphorus is precipitated with metallic salts. The mass, after passing through a polishing zone where a portion of the slurry is bioconverted to a humus, is used as a fertilizer for the soil.
An animal feed supplement, fertilizer or fuel is the result of the waste treatment process described in U.S. Pat. No. 5,535,528, where yard waste is mixed with waste animal sludge and dried to form an aggregate. The waste is treated in a thermal dryer with an inlet temperature from about 800xc2x0 F. to about 1300xc2x0 F. and an outlet temperature from about 200xc2x0 F. to about 350xc2x0 F. in order to partially dry the material and to make it virtually free of active pathogens, suggesting that all pathogens are killed in this drying step. The invention described in U.S. Pat. No. 5,811,014 relates to a method of sterilizing and sanitizing a hazardous flowable waste stream, which, while it would include human sewer waste, also describes sanitizing human blood, diseased human cells, and various hospital wastes. The process involves neutralizing the charge of the waste molecules so that they separate from each other for more efficient treatment and then exposing the liquid to ozone, electron-beam radiation and then ultraviolet radiation with more ozone through ultraviolet radiation to oxidize waste. Ultraviolet radiation and the formation of ozone through ultraviolet radiation to oxidize waste is employed in U.S. Pat. No. 5,897,785 prior to forming a semi-dry polymerized solid from the reaction product of the waste and high charge cationic polymers which is packaged for use as a fertilizer produced from animal waste.
U.S. Pat. Nos. 4,121,539, 4,354,936, 5,637,219, and 5,863,434 all describe using an anaerobic digester to produce methane from the animal waste treating process, but with varying degrees, if not discouraging degrees, of success.
The problem solved by the instant invention is the capability of processing animal manure to recover the significant protein values from the excrement which can be safely fed to animals to create weight increase. For instance, it is well-known that upon standing, the protein values of the manure, particularly poultry manure, will break down and dissipate with the passage of time. Therefore, in order to stabilize the protein present in the manure, it is important to sterilize such manure promptly to halt the bacterial degradation of the protein and to kill the incipient pathogens.
While the foregoing attempts have been made to treat solid animal waste to create a useful product widely acceptable, none have been totally successful and certainly virtually none have accomplished the conversion of protein in animal manure to high protein animal feed in the economically-sound manner of the instant invention.
The successful economic development of high-protein animal feed is accomplished by following the process described herein. In the first place, manure is collected and brought to the facility for treatment. This manure can be excrement from poultry, swine, or beef operations. It can originate at a single chicken coop or a cattle feedlot with thousands of head of cattle. Normally, in large operations the manure will end up being in the form of a slurry because of the necessity of flushing the excrement into a sump from which it can be moved to the process equipment usually based on the premises. If not ready, a slurry is formed. The use of the process of this invention can be made either at a central location where the animal waste is brought in trucks such as vacuum trucks used to xe2x80x9csuck upxe2x80x9d waste or unwanted materials. The treatment process can be connected integrally to the animal containment areas and receive the waste, usually in the form of a slurry.
The slurry containing the waste is held in a xe2x80x9cday tankxe2x80x9d for several days, preferably two to four days, to allow the oxygen to react or dissipate. Afterwards it is put in an anaerobic digester system operated at an elevated temperature of from about 35xc2x0 C. to about 65xc2x0 C. to cause the production of methane gas, and to some extent, carbon dioxide. The methane generation is important because the methane is captured and used to generate electricity and steam to support operation of the overall process of preparing the high-protein animal feed.
After the digestion and gas release and recovery, the slurry, having from about 45% to about 65% solids, by weight, is passed through a belt press or screw press to lower water content down to approximately 25% to 45% (65% to 75% solids). This water may be piped back to the slurry make-up step before the holding tank or to the anaerobic digester to be used as make-up water or passed on to filters before release into the environment. The solids from the filters form a compost which moves to the microwave dryer for processing and sterilizing.
The remaining solids in the form of a feed compost (after the free water is removed by the pressing process) are then conveyed to the microwave/hot air dryer for sterilization and drying down to a solids content of about 88% or over (water content from about 10% to about 12%). The microwave dryer is a vessel charged by radio frequency waves from about 915 MHz to about 2,450 MHz and is applied with outputs of 10 KW to 80 KW transmitter. The hot air for the dryer is supplied by output of hot exhaust gases from a turbine generator and/or a methane-burning heater, both utilizing methane gas generated by the anaerobic digesters.
At this point, the manure is sterilized and is substantially dry, and once sized through a series of screens, can be packaged for sale and distribution. Preferably, the course, more crunchy product would be packaged for large animal feed with the fines being packaged either for poultry or fish feed, or for use as plant fertilizer.
The methane recovered, can be processed to remove the carbon dioxide present as an anaerobic biogas co-product to enhance the heating value of the methane, even though it is not necessary to remove the carbon dioxide to create a more valuable methane. Depending upon the location of the facility and the overall amount of manure which can be treated, there may actually be excess methane produced to allow the sale of methane or electricity on the consumer market. This, of course, would depend upon the adequacy of storage facility on the location or the proximity of a pipeline or electrical lines.
The foregoing invention will be more completely described in the discussion which follows, it being manifest that there are many advantages to the practice of the invention including the upgrading of a troublesome waste to a valuable commodity and the recovery of a valuable energy resource.